Process of stabilizing thermoplastic knitted fabric containing cellulose ester yarns with superheated steam



1957 B. s. SPRAGUE El AL 2,777, 5 PROCESS OF STABILIZING THERMOPLASTICKNIT-TED FABRIC CONTAINING CELLULOSE ESTER YARNS WITH SUPERHEATED STEAMFiled NOV. 13, 1952 3 Sheets-Sheet 1 w {j m INVENTORS. (\1 v a? v BASILS.SPRAGUE MURRAY N.CARROLL kn 7 ROBERT H. ROUGHSEDGE I I I 1 I I IATTORNEYS.

, 2,777,750 FABRIC CONTAINING 5 WITH SUPERHEATED F 19:17 B. s. SPRAGUEETA].

PROCESS OF STABILIZING THERMOPLASTIC KNITTED CELLULOSE ESTER YARN STEAMFiled Nov. 13, 1952 3, Sheets-Sheet 2 E I \N .1 \N .EOD Iv .5 RE I RGRSS AA H TRCG N WNW m u i 19 za R J m mH m Q N N mm N. mw In. 1| III 8 Pl4F 1 1|. 1 PH 1 ll 1 1 1 d Ill R Q d u N N1 u N N. v 4 M P1 mm mm 8 l mN 3 i w J a 5 mm d- H 1 E mm A o a @N M +N 3 a 3 WM 1957 I B. s. SPRAGUEETAI. ,7 7,

PROCESS OF STABILIZING THERMOPLASTIC KNITTED FABRIC CONTAINING CELLULOSEESTER YARNS WITH SUPERHEATED STEAM Filed Nov. 13, 1952 v 3 Sheets-Sheet3 INVENTORS. BASIL S. SPRAGUE' MURRAY N. CARROLL V ROBERT H- ROUGHSEDGEBY (W ATTORNEYS.

United States PROCESS OF STABILlZING THERMUPLASTIC KNITTED FABRIC(IONTAWENG CELLU- ggggESl'ER YARNS WITH SUPEREATED 9 Claims. (Cl. 8-131)62.3265.- N. 3., New

This invention relates to the treatment of textile fabrics and relatesmore particularly to a process and apparatus for the treatment ofknitted fabrics containing yarns of cellulose acetate or other organicacid esters of cellulose.

It has long been known that knitted fabrics contm'ning yarns ofcellulose acetate or other organic acid esters of cellulose exhibit acertain degree of dimensional instability when subjected to launderingprocesses. When garments made of Warp knitted cellulose acetate arelaundered in water at 140 F. and then dried Without stretching, theirdimensions may change as much as 30% in width and 10% in length, thelength direction denoting the direction in which the fabric is fort. edduring knitting. The extent of such dimensional change depends, in part,on the manner in which the garment is finished after laundering, i. e.ironing or pressing. Mainly, however, the extent of dimensional changedepends on the previous treatment of the fabric, for example thetreatment of the fabric during and after the scouring and dyeingoperations. Customarily these scouring and dyeing operations areconducted in hot aqueous baths. If the wet knitted fabric leaving suchbaths is dried without stretching, the resulting fabric is commerciallyunacceptable for most uses, since the wales of the fabric are drawntogether and are directly in contact with one another, thereby greatlyreducing the width of the fabric. Accordingly, it has been customary totreat the wet fabric coming from the dyeing operation by stretching iton a tenter frame and drying it, while stretched, to a low moisturecontent, such as a moisture content of less than 6% based on the bonedry weight of the fabric, i. e. less than 6% regain. This processintroduces internal stresses into the yarns comprising the knittedfabric, and when the fabric is laundered, or subjected to other Wetatntting and mechanical working treatment, the fabric tends to return to itsformer configurations and dimensions. Such dimensional change ismanifestly undesirable.

It is an important object of this invention to provide a process andapparatus for the treatment of knitted fabrics containing yarns ofcellulose acetate or other organic acid esters of cellulose which willovercome the foregoing and other difiiculties and which will beespecially efiicient in operation.

A further object of this invention is the provision of a process andapparatus for the treatment of knitted fabrics containing yarns ofcellulose acetate or other organic acid esters of cellulose which willimpart to said fabrics a high degree of dimensional stability.

Other objects of this invention, together with certain details ofconstruction and combinations of parts of the apparatus, will beapparent from the following detailed description and claims.

According to the present invention, a knitted fabric containing yarns ofcellulose acetate or other organic acid esters of cellulose carrying afilm of liquid water is raised to an elevated temperature in a gaseousatmoswhile the fabric is held to phere, preferably of steam,

fabric is supported througha definite width and while the outsubstantially its entire area. The wet fabric is maintained at theelevated temperature until the cellulose acetate or other organic acidester of cellulose of which the yarns are composed is swollen and anyinternal stresses in the yarns are released, but care should be taken soas not to cause the yarns or the fibers making up the yarns to fuse orcoalesce one with the other. During this treatment the moisture contentof the fabric should not fall below its saturation regain value, whichis defined as the moisture regain value of the fabric in contact with anatmosphere of relative humidity at the temperature of the fabric. Thefabric is cooled and, if desired, dried. Following this treatment, it isfound that the fabric exhibits a high degree of dimensional stability sothat garments made of said fabric will, from a practical viewpoint,retain their shape and dimensions substantially unchanged during normaluse.

In our preferred procedure, a wet knitted fabric of cellulose acetate issubjected to superheated steam, and the moisture content of the fabricbefore contact with the superheated steam and the time of contact withthe superheated steam are so regulated that the excess surface moistureon the fabric is not completely evaporated and the moisture content ofthe fabric does not fall below its saturation regain value. That is,despite the evaporation of some of the water due to the drying effect ofthe superheated steam, an excess of water is maintained on the surfaceof the yarns throughout the exposure to the superheated steam.Thepresence of this excess of water is critical. If the moisture contentof the fabric is below the 100 C. saturation regain value when it isfirst placed into contact with the superheated steam, adequatedimensional stability will not be obtained. if, on the other hand,through evaporation the moisture content drops below the saturationregain value during contact with the superheated steam the yarns ofcellulose acetate will deluster.

Since the 100 C. saturation regain value of cellulose acetate yarns isgenerally about 14% to 16%, the fabric advantageously should have awater content prior to steam treatment of at least about 20% by weight,preferably at least 50% byweight, based on the weight of the driedfabric, to insure that the water content of all portions of the fabricis above the minimum value, thereby avoiding dry spots whose dimensionalstability will differ from that of the remainder of the treated fabric.The maximum water content of the fabric should normally not exceed aboutby weight to avoid the necessity of heating large quantities of water toan elevated temperature during the steam treatment. Moreover, it isdifficult to distribute such larger quantities of water in a uniformmanner throughout the fabric before the treatment with steam. Thepresence of uniformly distributed larger quantities of water in thefabric will, however, not interfere with the successful treatment of thefabric to impart a high degree of dimensional stability thereto. Thedesired amount of water may be added to a dry knitted fabric to prepareit for treatment in accordance with the process of this invention.Commercially, however, the process is best applied to the fabricimmediately following the final liquid treatment constituting a step inthe finishing of the fabric. For example, the fabric in its wetcondition following a wet finishing treatment is first treated to reduceits water content to the desired level, as by centrifuging, and thenstretched by about 5 to 30% to a definite width before being subjectedto the heat treatment in the manner set forth above. Not only doescarrying out the process of this invention following the final liquidtreatment in the finishing of the fabric effect important economies, butit also produces a fabric having the highest degree of dimensionalstability since the said 3 fabric is not subjected to any furtherstresses while in a hot, wet state before it is processed into garments.If desired, the knitted cellulose ester fabric while being stabilizedmay have thereon any of the softening and antistatic, finishes usuallyapplied to such fabrics.

As stated, the wet fabric is treated, in accordance with this invention,with steam while it is held to a definite width and while it issupported throughout substantially its entire area. One form ofapparatus for carrying out this treatment comprises a chamber providedwith an inlet and exit slot, through Which the fabric enters and leavesthe chamber, and equipped with tenter chains for holding the fabric to adefinite width and moving the fabric continuously through the chamber.There are also provided in the chamber, between the tenter chains, aplurality of rubber covered rollers for supporting the fabric throughoutsubstantially its entire area. The rollers are positively driven'so asto have a peripheral speed substantially equal to the linear speed ofthe fabric moving through the chamber so that no stresses will beapplied to said fabric. Instead of rollers, other means such as screens,belts or the like may be used to support the fabric during thetreatment. As the fabric moves through the chamber it is treated withsteam which is advantageously introduced into the chamber throughdistributing heads positioned both above and below the fabric at aplurality of points spaced along the path of the fabric. The steamraises the temperature of the fabric to a point where the wet celluloseacetate or other organic acid ester of cellulose comprising the yarns ofthe fabric is swollen and in a condition in which the internal stressesin the yarns are released rapidly. This temperature is preferably about100 C. The steam treatment should, however, not be continued to a pointwhere the yarns or the fibers making up the yarn tend to coalesce orwhere the hand of the fabric in changed in an undesirable manner. It isessential that the fabric be supported throughout its entire area whileit is at this elevated temperature. If no such support is provided, thefabric will tend to sag and be distorted due to its weight, therebyintroducing stresses which will be locked into the fabric during thetreatment and will cause dimensional changes in the fabric during use.

The superheated steam, which is desirably at atmospheric pressure and ata temperature above about 230 F.', preferably in the range of about 240F. to 250 F., is admitted to the chamber through a plurality ofopenings. The spacing of the openings throughout the chamber is suchthat there is obtained an even distribution of steam throughout the areaof the chamber. Moreover, the entering steam is caused to impinge on thefabric at fairly high velocity so as to effect an efiicient transfer ofheat to the fabric. In addition, a very even-steam distribution isnecessary because of the previously described hazard of delusteringwhich occurs if the fabric is over dried at any point during passagethrough the stabilization chamber. The waste steam is exhausted from thechamber by means of exhaust ducts mounted at the side of the chamber. 7

- In order to prevent the inrush of cool atmospheric air to the chamber,the exhaust rate is adjusted so that the rate of removal of spent steamat the exhaust ducts does not quite balance the input rate. That is,more steam is admitted to the chamber than is removed through theexhaust ducts. Hence, during operation a small amount of steam escapesthrough the slots through which the fabric enters and leaves thechamber. In addition, these exit and inlet slots have mounted, above andbelow, slotted. conduits through which heated air is forced. Theseconduits are mounted and aligned so that the heated air from the slotsforms an air curtain through which the fabric passes. This air curtainfurther serves to dilute the-escaping steam and prevent condensation onthe surrounding equipment. If desired, the wet fabric may be preheatedin any desired manner to an elevated temperature below the stabilizingtreatment temperature prior to its entry into the chamber so as toreduce the period of time needed for the steam to bring the fabric tothe treatment temperature. The time of treatment varies, depending uponalarge number of factors, including the percentage of water presentinitially in the fabric, the temperature at which the Wet fabric entersthe chamber, the weight of the fabric, the steam temperature, the degreeof suprheat and the like. Control of the time of treatment is effectedby adjusting the rate at which the fabric passes through the chamber,that is, by regu lating the speed of the tenter chains.

Following the steam treatment, the fabric is cooled. At least during thepreliminary stages of the cooling, the fabric should be held to adefinite width and supported throughout its entire area so as to avoidimposing stresses upon the hot fabric. Cooling may be eifected simply bypassing the fabric through the air, or, if desired, the rate of coolingmay be accelerated by passing a stream of cool air over the fabric.

During the treatment of the wet fabric with superheated steam, at leasta portion ofthe water in the fabric will be driven oif. After thecooling of the fabric is completed, any further drying of the fabricthat may be necessary is carried out by passing the fabric through adryer of any desired type. It is preferred to reduce the moisturecontent of the cellulose acetate to about 5 to 7% regain. Over-dryingtends to impart an objectionably harsh hand to the fabric. The driedfabric exhibits a high degree. of dimensional stability and is eminentlysuited for a Wide variety of applications.

A preferred embodiment of the 'apparatusof this invention is shown inthe accompanying drawings wherein: Fig. 1 is a side view of theapparatus, partly in section, Fig. 2 is a cross-sectional view of theapparatus, taken on the line 2-2 in Fig. l, in the direction of thearrows, Fig. 3 is a cross-sectional view of the apparatus, taken on theline 3-3 in Fig. l, in the direction of the arrows, Fig. 4 is a detailview of the upper steam distributor, and

Fig. 5 is a detail view of the lower steam distributor. Referring now tothe drawing, the reference numeral 11 designates a fabric whose edgesare secured to tender chains 12 that act to hold the fabric at adefinite width. The tenter chains 12 are mounted on supports, indicatedgenerally by reference numeral 13, that may be operated by means of handwheeis 14 to adjust the lateral spacing between the tenter chains 12in'a manner Well known in the art. The tenter chains 12 carry the fabric11 between a pair of heaters 15 equipped with infra-red heating elementsto effect a preheating of the said fabric. The

I fabric 11 is then moved by the tenter chains 12 into a 'treatingchamber, indicated generally by reference numeral 16. The treatingchamber 16 comprises a shell 17 that is supported on. a framework 18.The top 19 and upper portion of the ends 21 of the shell 17 are ofdouble wall construction and a heating fluid such as steam is passedthrough said walls to raise them to an elevated temperature so that nowater will condense on said walls to drop onto the fabric 11. Positionedin the chamber 16 are a plurality of rubbe covered rolls 22 that extendtransversely of the chamber between the tenter chains 12 and act tosupport the fabric during its treatment. The rolls 22 are driven at aperipheralspeed equal to the linear speed of the tenter chains 12 bymeans of a motor 23 through a variable speed drive 24, a chain 25 and aseries ofchains 26 and sprockets 27 that act to interconnectall'saidrolls. Steam is introduced into the chamber 16 through a plurality oflower distributors, indicated generally by reference nu-. meral 28, thatare positioned between the rolls 22 beneath the fabric 11, and aplurality of upper distributors, indicated generally by referencenumeral 29, that :are positioned above the fabric 11. 7 i

"Each of the lower distributors 28 -compnses a conduit 31 supported on apedestal 32 (Fig. and having, a slot 33 extending through theuppermostportion thereof for the discharge of the steam which issupplied to-said lower distributors from headers 34. The upperdistributors 29 each comprises an elongated rectangular enclosure 35 towhich steam is supplied by headers 36 through conduits 37. Extendinglongitudinally of the enclosure 35 are partitions 38 having apertures 39therein which act to distribute the steam emerging from the conduits 37more uniformly. To insure that there will be no drops of water in thesteam emerging from the upper distributors 29 to fall on and spot thefabric 13, there are provided a pair of conduits 41 extending the fulllength of the enclosure 35 and being spaced apart a short distance toprovide a passageway 42 therebetween. A heating fluid, such as steam,which may be at a higher temperature than the steam in the headers 36,is introduced into the conduits .1 from a header 43 and is dischargedfrom said conduits through a header 44. All the steam flowing throughthe passageway 42 will come into intimate contact with the heatedsurfaces of the conduits 41. thereby turning into steam any drops ofwater that may be present in the steam emerging from the headers 36.Moreover, when the steam which is at super-atmospheric pressure in theheaders 34 and 36 enters the chamber 15, which is at approximatelyatmospheric pressure, the essentially adiabatic drop in the pressure ofthe steam will impart a degree of superheat thereto and tend toeliminate water droplets therefrom.

If atmospheric air were permitted to enter into the chamber 16 freelytogether with the fabric 11, there would be a tendency for the coldatmospheric air to cause water to condense on all surfaces adjacent theentrance passageway. To avoid this possibility, there are providedadjacent the entrance and exit passageways pairs of conduits 45 and 45having slots 46 and 46' therein that face toward the fabric 11. Heatedair under pressure is introduced into the conduits 45 and 45' and flowsthrough the slots 46 and 46' toward the fabric 11 thereby acting as anair curtain to prevent the flow of cold atmospheric air into the chamber16 and also acting to assist in the preheating of the said fabric. Thechamber 16 is provided with exhaust ducts 47 through which pass aconstant flow of steam together with any air that may enter into thechamber during operation.

Upon leaving the chamber 16, the fabric 11 passes through a coolingsection, indicated generally by reference numeral 48. in at least thefirst portion of the cooling section 48, the fabric 11 is held at adefinite width and. supported throughout substantially its entire areain the same manner as during its passage through the chamber 16, namelby the tenter chains 12 and rolls 22. Cooling of the fabric 11 may beeffected simply through the action of atmospheric air. However, ifdesired, means such as slotted conduits, fans or the like may beprovided for producing a forced flow of a cooling medium, such as air,over the fabric 11 and, if even more rapid cooling is desired, thecooling medium may be refrigerated.

The fabric 11, after cooling, is carried by the tenter chains 1: into adryer 49 of any type. Means may be provided for supporting the fabricthroughout its entire area as it passes through the dryer 49, althoughthis has been found unnecessary when the drying conditions are notsevere. When the temperature and other drying conditions are such as toreduce the moisture content below about 4% regain, such supporting meansis desirable to prevent the introduction of a small, but not highlyobjectionable, degree of dimensional instability into the fabric 11. ifthe drying conditions are not so severe and fabric supporting means arenot employed in the drier, the lateral spacing between the tent-erchains 12 may be widened slightly, e. g. by about 4%, as these chainspass through the drier, in order to avoid any substantial sagging of thefabric in the drier. a

p The following example is givento illustrate in.- vention further.

Example- A large number ofpieces of fabric warp knittedof 55 denieryarns of cellulose acetate having an acetyl value of 54.5%, measured ascombined acetic acid, are scoured, dyed and washed and are thencentrifuged to bring their moisture content to about based on the dryweight of the fabric. The wet fabrics, which are at room ternperatureand have a width of about 90 inches, are sewn end to end and are thenpassed one after another through the apparatus shown in the drawings,without using preheater 15, at the rate of about 1300 pounds of wetfabric per hour while the fabrics are maintained at a width of illinches and while saturated steam at: a pressure of 150 pounds per squareinch gauge is passed at therate of about 5,000 pounds per hour through athrottling valve (not shown), through which it expands in an essentiallyadiabatic manner into the conduits leading to the lower distributors 28,upper distributors 29 and conduits 41. The overall temperature of thetreating chamher is above 230 F. After a treatment time of 15 seconds,the fabric is cooled and dried. The dried fabrics, when laundered in anautomatic washer at F. and dried in substantially tensionless condition,exhibit an average area shrinkage of less than 4%. Subsequent launderingefiects no appreciable change in dimensions. When similar pieces of thesame fabric are finished and dried in conventional manner they exhibitan average area shrinkage of 15% to 30% after the first washing.

While the process of this invention has been described specifically inconnection with the treatment of fabrics containing cellulose acetateyarns at the present time, it may also be employed for the treatment ofthe fabrics containing yarns of othr organic acid esters of cellulosesuch as, for example, cellulose propiouate, cellulose butyrate,cellulose acetate propionate and cellulose acetate butyrate.

it is to be understood that the foregoing detaileddescription is givenmerely by way of illustration and'that many variations may be madetherein without departing from the spirit of our invention.

Having described our invention, What We desire to se' cure by LettersPatent is:

l. A process for improving the dimensional stability of knitted fabriccontaining a thermoplastic lower aliphatic acid ester of cellulose yarnswhich comprises subjecting said knitted fabric, wetted with at least 20%of water based on the weight of the dried fabric, to superheated steamhaving a temperature above about 233 F, maintaining said fabric at adefinite width and at a moisture content above the saturation regainvalue of said cellulose ester throughout the treatment'with superheatedsteam, said treatment with superheated'steam being continued until saidcellulose ester is swollen and the internal stresses in the yarns arereleased and the dimensions of the fabric are stabilized to subsequentwashing, the time and temperature of said treatment being insuiicient toefiect fusion or coalescence of said yarns, removing the fabric fromcontact with the superheated steam before the moisture content of saidcellulose ester has been reduced below said saturation regain value sothat said fabric still carries an excess of water on the surface of saidyarns, and cooling the treated fabric, said fabric being supportedthroughout substantially its entire area while it is subjected to thesuperheated steam.

2. A process for improving the dimensional stability of knitted fabriccontaining cellulose acetate yarns which comprises subjecting saidknitted fabric, wetted with at least 20% of Water based onthe weight ofthe dried fabric, to superheated steam having a temperature above about230 F., maintaining said fabric at adefinite width and at a moisturecontent above the saturation regain value of said cellulose esterthroughout the treatment with superheated steam, said treatment withsuperheated steam being continued until said cellulose ester is swollenand the internal stresses in the yarns are released and the dimensionsof the fabric are stabilized to subsequent washing, the time andtemperature of said treatment being insufficient to efiect fusion orcoalescence of said yarns, removing the fabric from contact with thesuperheated steam before the moisture content of said cellulose esterhas been reduced below said saturation regain value so that said fabricstill carries an excess of water on the surface of said yarns, andcooling the treated fabric, said fabric being supported throughoutsubstantially its entire area while it is subjected to the superheatedsteam.

3. A process for improving the dimensional stability of knitted fabriccontaining yarns of cellulose acetate having a saturation regain valueat 100 C. of about 14 to 16% which comprises subjecting said knittedfabric, wetted with at least 50% of water, based on the weight of thedried fabric to superheated steam having a temperature above about 230F., maintaining said fabric at a definite width and at a moisturecontent above the saturation regain value of said cellulose esterthrough out the treatment with superheated steam, said treatment withsuperheated steam being continued until said cellulose ester is swollenand the internal stresses in the yarns are released and the dimensionsof the fabric are stabilized to subsequent washing, the time andtemperature of said treatment being insufiicient to effect fusion orcoalescence of said yarns, removing the fabric from contact with thesuperheated steam before the moisture content of said cellulose esterhas been reduced below said saturation rgain value so that said fabricstill carries an excess of water on the surface ofsaid yarns, andcooling the treated fabric, said fabric being supportedthroughoutsubstantially its entire area while it is subjected to thesuperheated steam.

4. A process for improving the dimensional stability of knitted fabriccontaining cellulose acetate yarns which comprises subjecting saidknitted fabric, wetted with at least 20% of water based on the weight ofthe dried fabric, to superheated steam having a temperature above about230 F., maintaining said fabric at a definite width and at a moisturecontent above the saturation regain value of said cellulose esterthroughout the treatment with superheated steam, said treatment withsuperheated steam being continued until said cellulose ester is swollenand the internal stresses in the yarns are released and the dimensionsof the fabric are stabilized to subsequent washing, the time andtemperature of said treatment being insufficientto effect fusion orcoalescence of said yarns, removing the fabric from contact with thesuperheated steam before the moisture content of said cellulose esterhas been reduced below said saturation regain value so that said fabricstill carries an excess of water on the surface of said yarns, andcooling the treated fabric, said fabric being supported throughoutsubstantially its entire area while it is subjected to the superheatedsteam, said superheated steam being applied to both the upper and lowersurfaces of said fabric.

5. A process for improving the dimensional stability of knitted fabriccontaining a thermoplastic lower aliphatic acid ester of cellulose yarnswhich comprises subjecting said knitted fabric, wetted with at least 20%of water based on the weight of the dried fabric, to superheated steamhaving a temperature above about 230 F, maintaining said fabric at adefinite width and at a moisture content above the saturation regainvalue of said cellulose ester throughout the treatment with superheatedsteam, said treatment with superheated steam being continued until saidcellulose ester is swollen and the internal stresses in the yarns arereleased and the dimensions of the fabric are stabilized to subsequentwashing, the time and temperature of said treatment'being insufiicientto effect fusion or coalescence of saidyarn, removing the fabric fromcontact with the superheated steam before the moisture content of saidcellulose ester has been reduced below said saturation regain value sothat said such conditions that the number of wales per. inch of thefabric has been increased, which comprises stretching said fabric to adefinite width to decrease the number of wales per inch and subjectingsaid fabric containing 120%, based on the weight of the dried fabric, ofwater to superheated steam having a temperature above about 230 F.,maintaining said fabric at said definite width and at a moisture contentabove the saturation regain value of said cellulose ester throughout thetreatment with superheated steam, said treatment with superheated steambeing continued until said cellulose ester is swollen and the internalstresses, in the yarns are released and the dimensions of the fabric arestabilized to subsequent washing, the time and temperature of saidtreatment being insuflicient to effect fusion or coalescence of saidyarns, removing the fabric from contact with the superheated steambefore the moisture content of said cellulose ester-has been reducedbelow said saturation regain value so that said fabric still carries anexcess of water on the surface of said yarns, and cooling the treatedfabric, said fabric being supported throughout substantially its entirearea while it is subjected to the superheated steam.

7. A continuous process for improving the dimensional stability of warpknitted fabric containing cellulose acetate yarns after said fabric hasbeen subjected to hot Water under such conditions that the number ofwales per inch of the fabric has been increased, which comprisescontinuously stretching said fabric to a definite width to decrease thenumber of wales per inch and continuously subjecting said fabriccontaining 50120%, based on the weight of the dried fabric, of water tosuperheated steam having a temperature above about 230 F., maintainingsaid fabric at said definite width and at a moisture content above thesaturation regain value of said cellulose ester throughout the treatmentwith superheated steam, said treatment with superheated steam beingcontinued until said cellulose ester is swollen and the internalstresses in the yarns are released and the dimensions of the fabric arestabilized to subsequent washing, the time and temperature of saidtreatment being insuficient to effect fusion or coalescence of saidyarns, continuously removing the fabric from contact with thesuperheated i steam before the moisture content of said cellulose esterhas been reduced below said saturation regain value so that said fabricstill carries an excess of Water on the surface of said yarns, andcontinuously cooling the treated fabric, said fabric being supportedthroughout substantially its entire area whiie it is subjected to thesuperheated steam.

8. Process asset forth in claim 7 in which said cellulose acetate has asaturation regain value at C. of about 14 to 16% and the water contentof said fabric just before it is subjected to the superheated steam isat least 50%, based on the weight of the dried fabric.

9. Process as set forth in claim Sin which said fabric is supportedthroughout substantially its entire area dur- (References on followingpage) References Cited in the file of this patent UNITED STATES PATENTSSpooner July 16, 1935 Croft Mar. 25, 1941 Wedler Mar. 7, 1944 BengerDec. 26, 1944 Vincent et a1. Jan. 17, 1950 10 Helmus Feb. 28, 1950 DodgeOct. 10, 1950 OTHER REFERENCES Nisbet: American Dyestutf Reporter,October 31, 1949, pp. 773, 774.

Rayon and Synthetic Textiles, August 1950, p, 62.

6. A PROCESS FOR IMPROVING THE DIMENSIONAL STABILITY OF WARP KNITTEDFABRIC CONTAINING CELLULOSE ACETATE YARNS AFTER SAID FABRIC HAS BEENSUBJECTED TO HOT WATER UNDER SUCH CONDITIONS THAT THE NUMBER OF WALESPER INCH OF THE FABRIC HAS BEEN INCREASED, WHICH COMPRISES STRETCHINGSAID FABRIC TO A DEFINTE WIDTH TO DECREASE THE NUMBER OF WALES PER INCHAND SUBJECTING SAID FABRIC CONTAINING 50-120%, BASED ON THE WEIGHT OFTHE DRIED FABRIC, OF WATER TO SUPERHEATED STEAM HAVING A TEMPERATUREABOVE ABOUT 230*F., MAINTAINING SAID FABRIC AT SAID DEFINITE WIDTH ANDAT A MOISTURE CONTENT ABOVE THE SATURATION REGAIN VALUE OF SAIDCELLULOSE ESTER THROUGHOUT THE TREATMENT WITH SUPERHEATED STEAM, SAIDTREATMENT WITH SUPERHEATED STEAM BEING CONTINUED UNTIL SAID CELLULOSEESTER IS SWOLLEN AND THE INTERNAL STRESSES IN THE YARNS ARE RELEASED ANDTHE DIMENSIONS OF THE FABRIC ARE STABILIZED TO SUBSEQUENT WASHING, THETIME AND TEMPERATURE OF SAID TREATMENT BEING INSUFFICIENT TO EFFECTFUSION OR COALESCENCE OF SAID YARNS, REMOVING THE FABRIC FROM CONTACTWITH THE SUPERHEATED STEAM BEFORE THE MOSITURE CONTENT WITH THECELLULOSE ESTER HAS BEEN REDUCED BELOW SAID SATURATION REGAIN VALUE SOTHAT SAID FABRIC STILL CARRIES AN EXCESS OF WATER ON THE FURFACE OF SAIDYARNS, AND COOLING THE TREATED FABRIC, SAID FABRIC BEING SUPPORTEDTHROUGHOUT SUBSTANSTEAM.